1. Field of the Invention
The present invention relates to a bearing for supporting a rotating shaft in a fluid stream.
2. Description of the Prior Art
Downhole drilling motors of the positive displacement type, embodying a rotor and stator arrangement of the Moineau type illustrated and described in U.S. Pat. No. 1,892,217, are well known. The rotor in prior drilling motors has one lobe operating within a companion two lobe stator made of rubber or corresponding elastomer material, the rotor itself being a solid member. The rotor partakes of an eccentric or orbital pass around the axis of the stator, producing an excessive amount of vibration as a result of the orbiting speed of the rotor, combined with its relatively high mass due to its solid construction, resulting in a decreased life of the rotor and of the parts of the motor associated therewith.
The drilling weight of prior motor apparatus is transmitted through a bearing assembly to the motor shaft, this bearing assembly being lubricated by the drilling mud or other fluid pumped down through the string of drill pipe and through the motor itself. Since drilling mud is very often sand laden, the bearings are operating in an abrasive liquid, resulting in their relatively short life, limiting the time that the motor can be used in drilling a bore hole, with consequent requirements for moving the entire motor apparatus from the bore hole and replacement of a substantial number of its parts, or, for that matter, replacement of the entire motor unit. Because of the use of the solid rotor, a dump valve assembly is incorporated in the drilling string above the motor to allow the drilling fluid to fill the drill pipe as the apparatus is run in the bore hole and to drain from the drill pipe while coming out of the hole.
U.S. Pat. No. 3,112,801, entitled "Well Drilling Apparatus", incorporates therein a bearing which is pressed into a liner which in turn is pinned within a casing. A drill shaft extends through the casing and is supported by the bearing. The inner face of the bearing can have longitudinally extending grooves for conducting fluid to the lower thrust bearings. However, this bearing is not self-lubricating and does not provide shock absorbing means.
The present apparatus is provided with a bearing assembly in the drilling motor that is sealed against entry of external fluids and substances, such as the drilling mud. The bearing assembly is filled with oil maintained at a higher pressure than the pressure externally of the bearing assembly, thereby insuring clean oil acting upon the bearings themselves which contributes to the long life of the bearing assembly, enhancing its ability to transmit drilling weight from the drilling string and stator or housing portion secured thereto and to the drill bit, as well as its ability to resist radial or lateral motion of the motor shaft within the stator or housing.
The apparatus also provides a bearing assembly in a fluid drilling motor which is capable of safely transmitting greater drilling weights from the drill string and stator or housing to the drill bit. More particularly, a plurality of thrust bearings are used in which one of the bearings normally carries the weight being imposed on the drill bit up to a predetermined amount, an additional bearing being brought into operation to transmit drilling weight to be imposed on the bit in excess of the predetermined amount.